Twist - Twist (English spelling) torsion

Japanese: ねじれ(捩れ) - ねじれ（英語表記）torsion

Mathematical term. (1) Given a point P on a space curve C , take a point Q on C that is sufficiently close to P, and consider the quotient ⊿θ/⊿ s obtained by dividing the angle ⊿θ between the osculating plane of C at P and Q by the arc length ⊿ s of C from P to Q. If Q is brought infinitesimally close to P, then ⊿θ/⊿ s will usually have a limiting value, and this value is called the twist or torsion rate of C at P, and its reciprocal is called the torsion radius. The shape of the curve is determined when the curvature and torsion rate are given as functions of the arc length measured from a fixed point.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

数学用語。(1)空間曲線C上に1点Pが与えられたとき，Pに十分近いC上の点Qをとり，PとQにおけるCの接触平面のなす角⊿θをPからQまでのCの弧の長さ⊿sで割った商⊿θ/⊿sを考える。ここでQを限りなくPに近づければ，ふつうの場合⊿θ/⊿sは極限値をもつが，この値をPにおけるCのねじれ，またはねじれ率といい，その逆数をねじれ率半径という。曲率とねじれ率が定点から測った弧の長さの関数として与えられると曲線の形が決定する。

出典　株式会社平凡社世界大百科事典第２版について　情報

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